1. Field of Invention
The present invention relates to a hydraulic pressure supply system of an automatic transmission for a vehicle. More particularly, the present invention relates to a hydraulic pressure supply system of an automatic transmission for a vehicle which supplies all the oil generated at a low-pressure hydraulic pump and a high-pressure hydraulic pump to a high pressure portion when the high pressure portion requires a large amount of oil temporarily, for example at initial starting or occurrence of shifting event.
2. Description of Related Art
Recently, vehicle makers direct all their strength to improve fuel economy due to worldwide high oil prices and strengthen of exhaust gas regulations. Improvement of fuel economy may be achieved by improving power delivery efficiency, and the improvement of the power delivery efficiency may be achieved by minimizing unnecessary power consumption of a hydraulic pump.
A recent automatic transmission is provided with a low-pressure hydraulic pump and a high-pressure hydraulic pump so as to improve fuel economy. Therefore, hydraulic pressure generated by the low-pressure hydraulic pump is supplied to a low pressure portion (i.e., a torque converter, a cooling device, and a lubrication device), and hydraulic pressure generated by the high-pressure hydraulic pump is supplied to a high pressure portion (i.e., friction members selectively operated when shifting).
In further detail, general hydraulic pressure of the automatic transmission is generated for the low pressure portion (i.e., generated by the low-pressure hydraulic pump), and hydraulic pressure demanded by the high pressure portion is generated by the high-pressure hydraulic pump and then is supplied to the high pressure portion. Therefore, fuel economy may be improved by minimizing power consumption for driving the hydraulic pump, and noise and vibration may be reduced and durability may be improved by reducing load applied to the hydraulic pump.
After the hydraulic pressure generated at the low-pressure hydraulic pump is supplied to the high-pressure hydraulic pump, however, the high hydraulic pressure is generated at high-pressure hydraulic pump in a conventional hydraulic pressure supply system. Therefore, the oil supplied to the high pressure portion may be insufficient temporarily due to delay in RPM rise of the hydraulic pump at initial starting or occurrence of shifting event. Thereby, responsiveness may be deteriorated or friction members (i.e., clutch or brake) of the high pressure portion may be damaged.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.